If you have good credit, help a sister out!

🔫Delaware
Sorry, not that exciting. But I need a little guidence. I just got a credit card, so I could build my credit. My limit is $300, and I do work part time (will be working full time soon). 
I also have a baby. 
And a car. 
What should I spend the credit card money on? (Obviously things I need). But what would/do you do with your credit? 
I'm not sure how to ask this question in a better way sooo.. Hopefully some of you understand, lol